From the way you've described it, it sounds as if your plants have stretched. This happens when there is insufficient light and the plants stretch up for it. You either need more/better light or move the light you have closer to the plants. (that's assuming you're using artificial light, are you?)
If the plants are bending/falling over then get some small garden cains and tie the plants to them for support.
What is the weather like where you live? If you want to put the plants outside and it's pretty cold then do it gradually so you don't shock them. Like put them outside for about an hour a day and gradually increase it. If it's warm then it should be OK to put them straight out.
Plants usually need fertilizer about 3 to 4 weeks after they sprout. Go real easy with fertilizer, like 1/4 the dose of what it says on the pack for the first time and slowly increase it until you get to full strength. This applies to chemical fertilizers like miracle-gro etc.. You could use organic feeds if you wish.